The present invention relates to a process for the preparation of biaryls using active nickel, palladium or platinum catalysts.
Biaryl compounds, especially biphenyl compounds, are of commercial importance as fine chemicals, intermediates for pharmaceuticals, optical brightening agents and agrochemicals.
A frequently used method of synthesising biaryls is the Suzuki reaction, in which iodo- or bromo-aromatic compounds as well as aryl triflates and, more rarely, chloroaromatic compounds are reacted with aryl-, vinyl- or alkyl-boronic acid derivatives in the presence of palladium catalysts. An overview article describing this method is, for example, M. Beller, C. Bolm, Transition Metals for Organic Synthesis, Vol. 1, p. 208, VCH-Wiley, Weinheim 1998.
Suitable catalysts for use within the scope of the Suzuki reaction are generally palladium and nickel compounds. Despite the economic advantage of nickel catalysts, palladium catalysts are preferred over nickel catalysts because of their lower toxicity and their greater tolerance towards functional groups. In the case of the use of palladium catalysts, both palladium(II) and palladium(0) complexes are used in Suzuki reactions. According to the literature, there are formulated as the active catalytic species coordinatively unsaturated 14-and 16-electron palladium(0) species, which are stabilized with donor ligands such as phosphanes. In particular when more inexpensive educts such as aryl bromides or aryl chlorides are used, the addition of stabilizing ligands is required in order to achieve adequate catalytic activation of the starting materials.
The catalyst systems described for Suzuki reactions frequently exhibit satisfactory catalytic turnover numbers (TON) only with uneconomical starting materials such as iodoaromatic compounds and activated bromoaromatic compounds. Otherwise, in the case of deactivated bromoaromatic compounds (i.e. bromoaromatic compounds having xe2x80x9celectron-displacingxe2x80x9d substituents or sterically hindered bromoaromatic compounds), and especially in the case of chloroaromatic compounds, large amounts of catalystxe2x80x94normally over 1 mol. %xe2x80x94must be added in order to achieve commercially usable turnovers.
In addition, because of the complexity of the reaction mixtures, simple catalyst recycling is impossible, so that catalyst costs generally also stand in the way of commercial realization. Although catalyst systems based on water-soluble phosphanes give satisfactory catalyst activities for the industrially important reaction of 2-chlorobenzonitrile with p-tolylboronic acid, the catalysts contain expensive sulfonated phosphanes. Moreover, a number of chloroaromatic compounds cannot as yet be activated in a commercially satisfactory manner even with those catalysts.
More recent active catalyst systems are based on cyclopalladated phosphanes (W. A. Herrmann, C. Broxcex2mer, K. xc3x96fele, C. -P. Reisinger, T. Priermeier, M. Beller, H. Fischer, Angew. Chem. 1995, 107, 1989; Angew. Chem. Int. Ed. Engl. 1995, 34, 1844) or mixtures of sterically demanding arylphosphanes (J. P. Wolfe, S. L. Buchwald, Angew. Chem. 1999, 111, 2570; Angew. Chem. Int. Ed. Engl. 1999, 38, 2413) or tri-tert.-butylphosphane (A. F. Littke, G. C. Fu, Angew. Chem. 1998, 110, 3586; Angew. Chem. Int. Ed. Engl. 1998, 37, 3387) with palladium salts or palladium complexes.
However, inexpensive chloroaromatic compounds cannot generally be activated in a commercially satisfactory manner with those catalysts either, since the catalyst productivities (TON) are below 10,000 and the catalyst activities (TOF) are below 1000 hxe2x88x921. Accordingly, in order to achieve high yields in particular in the case of such industrially valuable starting materials, it is necessary to use comparatively large and hence very expensive amounts of catalyst. For example, the catalyst costs for the preparation of one kilogram of an organic intermediate having a molecular weight of 200 using 1 mol. % palladium catalyst are more than 100 US$ at current noble metal prices, which shows the necessity of improving catalyst productivity. Accordingly, despite all the further developments made to catalysts in recent years, only a small number of industrial reactions of the arylation of chloroaromatic compounds have become known to date.
For the reasons mentioned, there is a great need for new processes for the preparation of biaryls, which processes do not exhibit the disadvantages of the known catalytic processes, and for palladium catalyst systems suitable therefor which contain inexpensive ligands, which are suitable for implementation on an industrial scale and which yield the biaryls in a high yield, with high catalyst productivity and in high purity.
That object can be achieved by a process for the preparation of mono-, bi- or poly-functional biaryls of the general formula I
Arxe2x80x94Arxe2x80x2xe2x80x83xe2x80x83(I) 
by reaction of an aryl compound of formula II
Arxe2x80x94Xxe2x80x83xe2x80x83(II) 
with an arylboronic acid derivative of formula III
Arxe2x80x2xe2x80x94B(OR1)2xe2x80x83xe2x80x83(III) 
in the presence of a catalyst, which process is characterised in that the catalyst used is a metal complex of the general formula IV 
wherein in formulae I to IV
Ar and Arxe2x80x2 each independently of the other represents mono- or poly-cyclic aromatic that is optionally substituted as desired and has up to 14 carbon atoms in the ring, or heteroaromatic that is optionally substituted as desired and has from 5 to 10 atoms in the ring, of which up to four atoms independently of one another may be N, O or S,
X represents I, Br, Cl, OSO2CF3, OSO2(aryl), OSO2 (alkyl), N2+,
M represents nickel, palladium or platinum,
L represents a monodentate phosphoroorganic ligand PR6R7R8,
A, B, C each independently of the others represents oxygen, sulfur, CH2, C(R9)a(R10)b, N(R11)c, Si(R12)d(R13)e, wherein a, b, c, d, e may each independently of the others be 0 or 1, and when a, b, c, d, e of at least one of the radicals in question is 0, A, B and C may also be part of a ring system,
x, y, z represent 0 or 1 and x+y+z=from 1 to 3,
R1 represents hydrogen, alkyl, aryl or alkenyl, wherein in formula III B(OR1)2 may also form a ring system,
R6 to R8 have the meanings of R1, or represent O-alkyl, Oxe2x80x94C(O)-alkyl, O-(aryl), as well as groups of any desired condensed ring system,
R2 to R5.
and R9 to R13 have the meanings of R1, or represent O-alkyl, Oxe2x80x94C(O)-alkyl, O-(aryl), Oxe2x80x94C(O)-aryl, F, Cl, OH, NO2, Si (alkyl)3, CF3, CN, CO2H, C(O)H, SO3H, NH2, NH(alkyl), N(alkyl)2, P(alkyl)2, SO2(alkyl), SO(alkyl), SO(aryl), SO2(aryl), SO3 (alkyl), SO3(aryl), S-alkyl, S-aryl, S-alkenyl, NHxe2x80x94CO(alkyl), CO2(alkyl), CONH2, CO(alkyl), NHCOH, NHCO2(alkyl), CO(aryl), CO2(aryl), CHxe2x95x90CHxe2x80x94CO2(alkyl), CHxe2x95x90CHxe2x80x94CO2H, P(aryl)2, PO(aryl)2, PO(alkyl)2, PO3H, PO(O-alkyl)2, and groups of any desired condensed ring system,
xe2x80x83wherein alkyl represents hydrocarbon radical having from 1 to 10 carbon atoms and alkenyl represents mono- or poly-unsaturated hydrocarbon having from 1 to 10 carbon atoms, each of which may be branched and/or substituted by Cl, F, alkyl, O-alkyl, phenyl, O-phenyl, and aryl represents an optionally Cl-, F-, alkyl-, O-alkyl-, phenyl-, O-phenyl-substituted aromatic or heteroaromatic having from 5 to 10 atoms in the ring.
In the process according to the invention, aryl compounds of formula II are preferably reacted with arylboronic acid derivatives of formula III in which Ar and Arxe2x80x2 each independently of the other represents an optionally substituted phenyl, naphthyl, anthryl, phenanthryl or biphenyl.
In the process according to the invention, the aryl compounds used are preferably compounds of formula IIa 
wherein R14 to R18 have the meanings given for R2 to R5 and R9 to R13, and the arylboronic acid derivatives used are preferably compounds of formula IIIa 
wherein R19 to R23 have the meanings given for R2 to R5 and R9 to R13.
There are used as the catalyst in the process according to the invention especially metal complexes of formula IV that contain as the metal M preferably nickel and palladium, and especially palladium.
In the catalysts of formula IV, the diene component is particularly preferably diallyl ether, diallylamine, diallylmethylamine, N-acetyldiallylamine, diallyl sulfide, diallylsilane, diallyldimethylsilane, divinyldisiloxane, bis-([2]thienylmethyl) ether, bis-(2-cyano-3"xgr""xgr"-[2]furyl-allyl) ether, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, difurfuryl ether, difurfurylamine, bis(thiophen-2-yl-methyl)-amine, difurfuryl sulfide, 1,1,3,3-tetramethyl-1,3-dithien-2-yl-disiloxane, 1,1,3,3-tetramethoxy-1,3-divinyl-disiloxane, 1,3-dimethyl-1,3-divinyldisiloxanediol, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetra-siloxane, 1,3,5-trimethyl-1,3,5-trivinyl-cyclotrisiloxane, 1,3,5,7,9-pentamethyl-1,3,5,7,9-pentavinyl-cyclopentasiloxane, 1,3-divinylbenzene, 2,6-divinylpyridine and derivatives thereof.
The ligands L in the catalysts of formula IV are preferably trialkylphosphines and triarylphosphines. Special preference is given to tricyclohexylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, triphenylphosphine, tri-o-tolylphosphine, di-(1-adamantyl)-n-butylphosphine, di-(1-adamantyl)-isopropyl-phosphine, di-(1-adamantyl)-cyclohexylphosphine, 2-(dicyclohexylphosphino)biphenyl, 2-(dicyclohexylphosphino)toluene, N,N-dimethyl-2-(dicyclohexylphosphino)aniline, 2-(di-tert-butylphosphino)biphenyl, 2-(di-tert-butylphosphino)toluene, N,N-dimethyl-2-(di-tert-butylphosphino)aniline.
The process according to the invention is especially suitable for the synthesis of biaryls of formula I wherein aryl and arylxe2x80x2 represent a substituted phenyl, naphthyl, anthryl, phenanthryl, biphenyl radical or/and a five-, six- or seven-membered heteroaromatic radical optionally having nitrogen, oxygen or sulfur atoms in the ring. In the case of the heteroaromatic radicals, substituted pyridines, pyrimidines, oxazoles, imidazoles, pyrazines, quinolines, indoles, furans, benzofurans or/and thiophenes are particularly preferred.
The process according to the invention has proved especially suitable for the preparation of compounds of formula I wherein aryl and arylxe2x80x2 carry up to 4 substituents which may independently of one another be alkyl, O-alkyl, Oxe2x80x94CO-alkyl, N-alkyl2, phenyl, aryl, fluorine, chlorine, NO2, CN, COOH, CHO, SO2-alkyl, NH-alkyl, COO-alkyl, CONH2, CONH-alkyl, CO-alkyl, CO-phenyl and PO-phenyl2, wherein alkyl and aryl are as defined above.
In the process according to the invention, the catalyst is used in an amount of from 0.001 to 10 mol. % and preferably from 0.01 to 1 mol. %, based on the concentration of aryl compound or arylboronic acid derivative.
The process is normally carried out in a solvent. There are used as the solvent generally inert organic solvents and/or water. Especially suitable as solvents or solvent mixtures are water, aliphatic ethers, aromatic or aliphatic hydrocarbons, alcohols and esters. Examples of those especially suitable solvents are THF (tetrahydrofuran), dioxane, diethyl ether, diglyme (diethylene glycol dimethyl ether), MTBE (methyl tert-butyl ether), DME (ethylene glycol dimethyl ether), toluene, xylenes, anisole, ethyl acetate, methanol, ethanol, butanol, ethylene glycol, ethylene carbonate and propylene carbonate. However, dipolar aprotic solvents are also suitable, such as dialkylsulfoxides, nitrites, N,N-dialkylamides of aliphatic carboxylic acids or alkylated lactams. Examples thereof which may be mentioned are dimethylsulfoxide, acetonitrile, benzonitrile, N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.
The process is preferably carried out at temperatures of from 0 to 200xc2x0 C.; in many cases it has proved expedient to work at temperatures of from 40 to 180xc2x0 C., preferably at from 60 to 160xc2x0 C. The reaction can be carried out at a pressure of from 0.5 to 100 bar, with a pressure in the range from normal pressure to 60 bar preferably being used.
It is advantageous to carry out the reaction in the presence of a base. Suitable therefor are primary, secondary or tertiary amines, such as alkylamines, dialkylamines, trialkylamines, which may be alicyclic or open-chained. There come into consideration as bases also alkali metal or alkaline earth metal salts of aliphatic or aromatic carboxylic acids, especially acetates, propionates, benzoates, or alkali metal or alkaline earth metal carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, oxides or hydroxides.
It is also possible to use as bases in the process according to the invention metal alkoxides, especially alkali metal or alkaline earth metal alkoxides, such as sodium methanolate, potassium methanolate, sodium ethanolate, potassium ethanolate, magnesium methanolate, magnesium ethanolate, calcium ethanolate, calcium methanolate, sodium tert-butanolate or potassium tert-butanolate.
The base can have a positive effect on the progress of the reaction by activating the arylboronic acid to anionic boranate species. In addition to the above-mentioned bases, such an activation can also be achieved by the addition of fluoride salts such as, for example, caesium fluoride, calcium fluoride, sodium fluoride, potassium fluoride, tetraalkylammonium fluorides.
The base is advantageously used in an amount of from 0.1 to 5 mol.-equivalent, based on the concentration of aryl compound or arylboronic acid derivative.
The catalysts of formula IV that are used may either be employed in the form of molecularly defined compounds or prepared in situ by reaction of a metal diene precursor with a corresponding phosphoroorganic compound PR6R7R8. A catalyst precursor is, for example, a complex compound between the metal in oxidation stage 0 and one or more diene ligands R2R3Cxe2x95x90CHxe2x80x94Ax-By-Czxe2x80x94CHxe2x95x90CR4R5. Typical catalyst precursors are, for example, complexes of Pd(0) or Ni(0) with such dienes, it being possible for those dienes to coordinate in the catalyst precursor in both a monodentate and a bidentate manner.
It is a particular advantage of the catalyst systems to be used in the process according to the invention that preforming, that is to say the preliminary reaction to the active catalyst, is particularly simple to carry out, and that it is possible to work with a metal diene/phosphoroorganic compound ratio of 1:1. As a result, an excess of expensive phosphoroorganic ligands is avoided, working up is simpler, and more active catalysts are obtained.
When using chloroaromatic compounds, bromoaromatic compounds, aryl triflates or aryl mesylates and related starting materials, it is sometimes advantageous to add a co-catalyst to the catalyst. The co-catalyst may be a salt of a halogen, especially a halide of the alkali metal elements or alkaline earth metal elements, an ammonium halide, a tetraalkylammonium halide, a phosphonium halide and/or a tetraalkylphosphonium halide. The co-catalyst is preferably a fluoride, bromide or chloride. Special preference is given to calcium fluoride, tetrabutylammonium fluoride, caesium fluoride, potassium fluoride, sodium fluoride, lithium bromide, sodium bromide, potassium bromide, caesium bromide, lithium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, benzyltrimethylammonium bromide, benzyltrimethylammonium chloride, trioctylmethylammonium bromide, tetraphenylphosphonium bromide, tetraphenylphosphonium chloride.
The co-catalyst is used in an amount of from 0.01 to 500 mol. % and preferably from 0.1 to 300 mol. %, based on the amount of aryl compound or arylboronic acid derivative. Where it is advantageous in terms of the process, the reaction can also be carried out in the co-catalyst as solvent (salt melt).
With the process according to the invention it is possible to achieve turnover values of the catalysts of the order of 1,000,000 and above for bromoaromatic compounds as starting materials, and 10,000 and above for chloroaromatic compounds.
Accordingly, because of the catalyst activities, it is possible in the process according to the invention to use extremely small amounts of catalyst, so that the catalyst costs, especially where palladium catalysts are used, are not cost-limiting in comparison with conventional Suzuki reactions for the corresponding process.
The biaryls prepared according to the invention can be used commercially, for example as intermediates for pharmaceuticals (for example for AT II antagonists) and agrochemicals, as ligand precursors for metallocene catalysts, as optical brightening agents and structural units for polymers.